An electric power facility may comprise plural power production entities, such as wind turbines, which may be connected at a point of common coupling (PCC) to provide their generated power to an utility grid network. In the US the term PCC may refer to the connection between the grid operator and the local power producer. So a point of common coupling may be at the MV side if the grid company owns the transformer. It may be right on the other side of the transformer on the HV side or it may be miles upstream if the local power producer had to install a line to get out to the wind power plant.
The wind turbines may in particular be variable speed wind turbines which may, depending on a load on the grid, require some VAr (voltage ampere reactive) control, in order to enhance the power quality or to comply with the interconnection agreement at the point of common coupling.
U.S. Pat. No. 7,071,579 B2 discloses a wind farm VAr (voltage ampere reactive, also referred to as var) support controller and a harmonics filter controller for a wind farm connected to a grid. The var support and harmonics filter is applied at the low voltage side of the grid between the wind turbine transformer and the wind farm transformer which transforms the low or medium voltage to a high voltage according to local regulations. The voltage (VAr) support is applied at the production entities (turbines), at the MV side of the substation transformer or at the HV side of the substation transformer to satisfy the requirements at the PPC point.
U.S. Pat. No. 7,042,110 B2 discloses a variable speed wind turbine, wherein a generator converter of the wind turbine controls the generator torque by a field orientation method. And the grid converter controls the grid characteristics like MW, Voltage (MVAr or cos(φ)) However, the var controller and cos(φ) controller are not described in detail.
U.S. Pat. No. 7,606,638 B2 discloses a wind park with voltage control (MVAr or cos)φ)), wherein the park master has communication lines for controlling the wind energy installations in order to set the optimal combination of active capacitor banks and voltage references to the wind turbines to increase the power transmission to the network.
It has been observed that a power facility comprising plural power production entities may operate at less than optimal efficiency. Further, it has been observed that conventional control methods may not provide the flexibility to reach a higher level of efficiency
There may be a need for an electric power control system for controlling a plurality of plural power production entities which distributes voltage (MVAr or cos(φ)) references to the individual power production entities in order to improve the efficiency of the power production facility. Further, there may be a need for an electric power facility comprising an electric power control system improved in particular regarding the efficiency of the electric power facility. Further, there may be a need for an electric power facility efficiently providing power under varying load conditions.